A TIN is a set of triangles each with X,Y, and Z
coordinates. Because the points define a plane, it is easy to interpolate
an elevation at every point in the triangle from the corner coordinates.
TINS have been proposed as alternatives to DEMs or grids, but they have greater
storage requirement and more complicated indexing to rapidly find the triangle
that covers a particular point. Virtually no TINs have been produced by
mapping agencies.